Work performed during the past several years has indicated that the neuroendocrine control of growth hormone and prolactin secretion most likely involves both releasing and inhibiting factors of hypothalamic origin. As a consequence measurement of pituitary hormone levels in plasma alone is insufficient for determining which of the neuroendocrine control mechanisms is responsible for observed alterations in hormone secretion. Studies involving a multifaceted investigative effort will be continued to 1) Develop and refine sensitive and specific bioassays for each of the hypothalamic factors involved in controlling growth hormone and prolactin secretion using an in vivo rat model and an in vitro dispersed rat anterior pituitary cell culture system, 2) A search for the presence of releasing and inhibiting factors in peripheral venous blood, portal hypophyseal blood of patients undergoing pituitary surgery, and in cerebral spinal fluid of normal subjects and of patients with disorders of growth hormone or prolactin secretion. Pharmacologic agents which effect growth hormone and prolactin secretion by altering neurotransmitter function will be used in an attempt to demonstrate changes in the level of releasing and inhibiting factors in animals and humans.